1. Field of the Invention
The present invention relates to a sheet-member stacked structure; the present invention also relates to a lead frame which may be is used with one or more other lead frames to assemble a plurality of sheet members into a component of, e.g., an ink jet printer head or an electronic device; the present invention also relates to a sheet-member stacked and adhered structure in which a plurality of sheet members are stacked on, and adhered to, each other and which is employed by, e.g., an ink jet printer head or an electronic device; and the present invention also relates to an ink jet printer head and particularly to such a sheet-member-stacked-type ink jet printer head which has a plurality of ink ejection nozzles arranged in at least one array.
2. Discussion of Related Art
There is known a piezoelectric ink jet printer head including a channel unit constituted by a plurality of sheet members which are stacked on, and fixed to, each other with an adhesive and which have a plurality of ink channels including a plurality of pressure chambers; a piezoelectric actuator which applies a pressure to an ink accommodated by each one of the pressure chambers of the channel unit; and a cable member which transmits control data from an external device to the piezoelectric actuator.
The sheet members constituting the channel unit include a nozzle sheet having a plurality of ink ejection nozzles; a base sheet having the pressure chambers corresponding to the ink ejection nozzles; and a manifold sheet having a manifold chamber as a common ink chamber provided between an ink supply source and each of the pressure chambers.
The channel unit is assembled, i.e., the sheet members are stacked on, and fixed to, each other, in a method disclosed by, e.g., Japanese Patent Application Publication No. 2002-105410, in the following manner:
First, a plurality of lead frames of different sorts are prepared. Each of the lead frames includes a substantially rectangular frame portion; a plurality of sheet members of a same sort that are arranged inside the frame portion such that the sheet members extend substantially parallel to each other; and a plurality of bridge portions each of which has a small width and which integrally connect between the frame portion and the corresponding sheet members. Each of the lead frames is prepared by, e.g., etching, while simultaneously a prescribed ink-channel pattern such as a flow passage or a pressure chamber is formed in each of the sheet members of the each lead frame.
After the lead frames are prepared, an adhesive is applied to respective contact surfaces (i.e., respective planar surfaces) of the sheet members. Subsequently, positioning pins of a jig are inserted into positioning holes formed in the frame portion of each of the lead frames. Thus, the lead frames are stacked on each other in a prescribed order, while each group of sheet members that are arranged in a direction of stacking of the lead frames are positioned relative to each other. Then, a pinching force or a pressing force is applied to the uppermost and lowermost lead frames, so that each group of sheet members arranged in the stacking direction are adhered and fixed to each other and are thereby integrated with each other.
Next, the bridge portions are cut off so as to separate each group of integrated sheet members from the frame portions. Thus, a channel unit as a sheet-member stacked structure is obtained.
In the above-indicated ink jet printer head, each of the sheet members constituting the channel unit may have a substantially rectangular shape that is elongate in a direction in which the ink ejection nozzles are arranged, for the purpose of increasing the total number of the nozzles employed and thereby increasing a printing speed of the printer head.
In each of the conventional lead frames constructed as described above, two opposite short-side end portions (i.e., two opposite short sides) of each of the sheet members are integrally connected to the frame portion via the respective thin bridge portions, but two opposite long-side end portions (i.e., two opposite long sides) of the each sheet member are not connected to the frame portion or any other portion. Therefore, if two opposite long-side portions of the frame portion are grasped by a person's hand, e.g., when an adhesive is applied to the each lead frame or when the lead frames are stacked on each other, each of the sheet members may be so sharply curved or deformed as to have a generally V-shaped cross section as seen in a direction in which the sheet members are arranged inside the frame portion, depending upon the manner of grasping. In addition, when each lead frame is washed or when an adhesive is applied to the each lead frame, an external force may be exerted to each sheet member, so that the each sheet member may be curved or deformed as described above.
If the curved sheet members are stacked on each other, and are fixed to each other with the adhesive, then gaps or spaces may be left around the curved portions of the sheet members. Those gaps or spaces may cause defects such as ink leakage.
Meanwhile, there is also known a piezoelectric ink jet printer head including a channel unit in which a plurality of sheet members each having one or more ink channels are stacked on each other and are adhered to each other with an adhesive; a piezoelectric actuator which applies a pressure to the ink accommodated by each of a plurality of pressure chambers of the channel unit; and a cable member which transmits control information from an external device to the piezoelectric actuator.
Japanese Patent Application Publication No. 2002-96478 or its corresponding U.S. Pat. No. 6,536,879 discloses an example of the above-indicated channel unit. This channel unit includes a nozzle sheet having a plurality of ink ejection nozzles; a base sheet having a plurality of pressure chambers communicating with the ink ejection nozzles, respectively; two manifold sheets which cooperate with each other to define one or more manifold chambers which store the ink supplied from an ink supply source and deliver the ink to each of the pressure chambers; and a spacer sheet. The channel unit is assembled such that in a direction from the bottom to the top of the unit, the base sheet, the spacer sheet, the two manifold sheets, and the nozzle sheet are stacked on, and bonded to, each other in the order of description.
At least one of respective contact surfaces (i.e., respective planar surfaces) of each pair of adjacent sheet members that are located adjacent each other in the direction of stacking of the sheet members, has narrow relief grooves that are provided, separately from the pressure chambers or the manifold chambers, along locations where an adhesive is applied. The relief grooves do not extend through the thickness of each sheet member, and open in only one major surface thereof. In addition, each sheet member has air relief holes that are formed through the thickness thereof and communicate with the relief grooves. Thus, each relief groove communicates with ambient air, via the corresponding air relief hole or holes that opens or open in one of opposite major surfaces of the stacked sheet members that are opposite to each other in the stacking direction, but none of the air relief holes open in the other major surface of the stacked sheet members.
When the channel unit is assembled, first, the adhesive is applied to each of the respective contact surfaces of the sheet members, and then the base sheet, the spacer sheet, and the two manifold sheets are stacked on each other in the order of description in the direction from the bottom to the top.
Subsequently, a pinching force or a pressing force is applied to one of the two manifold sheets as the top sheet member and the base sheet as the bottom sheet member, so that the stacked sheet members are adhered and fixed to each other. During this operation, air, or air bubbles that is or are trapped in gaps left between the respective contact surfaces of each pair of adjacent sheet members, or is or are mixed with the adhesive, are discharged into the ambient air via the relief grooves and the air relief holes.
Then, the nozzle sheet is fixed, with the adhesive, to an outer surface of the stacked and adhered sheet members (i.e., an upper surface of the one manifold sheet as the top sheet member).
However, in the case where the viscosity of the adhesive used is too low or the amounts of the adhesive applied are too much, superfluous amounts of the adhesive may flow out of the air relief holes of the top sheet member, when the sheet members are pressed and bonded to each other. Conventionally, those superfluous amounts of the adhesive are wiped off after the sheet members are integrated with each other and before the nozzle sheet is adhered to the thus obtained integral structure. However, this operation is time-consuming and cumbersome.
In addition, the wiping operation may result in leaving some amounts of adhesive on the outer surface of the integral structure, i.e., the upper surface of the top sheet member. Since the adhesive left hardens around, e.g., the respective open ends of the air relief holes located in the outer or upper surface of the integral structure, and forms bosses, the degree of planarity or flatness of the outer surface of the integral structure is adversely lowered.
Since the superfluous adhesive hardens, and forms unevenness, on the outer surface of the stacked sheet members, i.e., lowers the degree of flatness of the upper surface of the integral structure, the thickness of the adhesive applied to the upper surface so as to adhere the nozzle sheet to that surface cannot be made uniform. This may lead to a defective adhesion of the integral structure and the nozzle sheet. If it is attempted to adhere the nozzle sheet to the outer surface of the integral structure suffering this problem, the nozzle sheet is likely to be warped or inclined, which adversely influences the ink ejecting performance of the ink jet printer head as a final product.
A conventional on-demand ink jet printer head, disclosed by, e.g., Japanese Patent Application Publication No. 2002-36545, and Japanese Patent Application Publication No. 2002-59547 or its corresponding U.S. Pat. No. 6,648,455, employs a channel unit which is constituted by a plurality of sheet members stacked on each other and has a plurality of ink channels. The sheet members include a nozzle sheet having a plurality of ink ejection nozzles; a base sheet having a plurality of pressure chambers communicating with the ink ejection nozzles, respectively; and a manifold sheet having a manifold chamber which is connected to an ink supply source, on one hand, and is additionally connected to each of the pressure chambers, on the other hand. The ink jet printer head additionally employs a piezoelectric actuator including a plurality of piezoelectric ceramic sheets and a plurality of internal electrode layers which are alternately stacked on each other. The internal electrode layers include a plurality of internal common electrodes and a plurality of internal-individual-electrode layers which are alternate with each other in the direction of stacking of the piezoelectric and electrode sheets. Each one of the internal-individual-electrode layers includes a plurality of internal individual electrodes. The internal individual electrodes of the internal-individual-electrode layers cooperate with the common electrodes to sandwich a plurality of portions of each of the piezoelectric sheets and thereby define a plurality of active portions of the piezoelectric actuator. The piezoelectric actuator is stacked on, and bonded to, the channel unit, such that the active portions of the piezoelectric actuator are aligned with the pressure chambers of the channel unit, respectively.
Generally, the above-indicated base sheet having the pressure chambers is constituted by a thin metal sheet, in particular, a rolled metal sheet, e.g., a rolled stainless steel sheet.
In the case where the pressure chambers are formed through the thickness of the base sheet, such that the pressure chambers are arranged in at least one array, a lengthwise direction of each of the pressure chambers is oriented parallel to a widthwise direction of the base sheet and the array of the pressure chambers is oriented parallel to a lengthwise direction of the same. The ink ejection nozzles are arranged at a very short interval of distance in a direction parallel to the lengthwise direction of the base sheet. For example, seventy two ink ejection nozzles are arranged over a length of 1 inch (i.e., 25.4 mm) in a staggered or zigzag fashion. Since the pressure chambers correspond to the ink ejection nozzles, respectively, a thickness of a partition wall located between each pair of adjacent pressure chambers that are located adjacent each other in the array is very small (e.g., from about 0.09 mm to about 0.10 mm). Hence, if the direction in which the pressure chambers are arranged in the array is parallel to the direction of rolling of the metal sheet constituting the base sheet, that is, if a direction perpendicular to the lengthwise direction of each pressure chamber is parallel to the rolling direction, the following problems are encountered:
When a thin metal sheet is produced by rolling, the rolled metal sheet is likely to have, in opposite major surfaces thereof, rolling marks or streaks extending in the rolling direction. Thus, the rolling streaks have irregularity in a direction perpendicular to the rolling direction. In other words, the rolling streaks include microgrooves and microridges each extending in the rolling direction. Therefore, a partition wall located between each pair of adjacent pressure chambers may have, in the opposite surfaces thereof, rolling streaks extending in the direction of arrangement of the pressure chambers. In this case, a thickness of each of respective adhesive layers that are applied to the opposite surfaces of each partition wall when the spacer sheet and the piezoelectric actuator are adhered to the opposite major surfaces of the base sheet, respectively, may not be made uniform because of the presence of microgrooves of the rolling streaks, and the adhesive layers may include such portions that have a very small, or even zero, thickness and provide gaps continuously connecting between the two adjacent pressure chambers along the opposite surfaces of the each partition wall. Therefore, some ink may leak between the two adjacent pressure chambers, and accordingly a droplet of ink may not be ejected from a desired ink ejection nozzle, so that an image may be recorded at an inappropriate position on a recording medium. Thus, the image cannot be recorded with accuracy.